Recently, the use of equipments related to information communication has increased drastically. Since unnecessary electromagnetic waves are radiated from electronic equipments and systems, it is reported that the mall function of the equipments and some fatal damage to human life occur.
For the countermeasure to the above, several regulations for the electromagnetic wave interference, have been enacted internationally by CISPR, FCC, ANSI, etc.
In the domestic case, the regulations related to the Electromagnetic Interference (EMI) and the Electromagnetic Susceptibility (EMS) have been established and enacted. For measurement of such EMI and EMS, an equivalent, free space from electromagnetic waves are required. As the means of the equivalent space, an anechoic chamber is widely used.
The Frequency range for EMI test was from 30MHz to 1GHz. However it was broadband from 1GHz to 18GHz additionally by CISPR 11 on November, 1998.
To construct in anechoic chamber for the above purpose, it is needed that the electromagnetic wave absorber has the capability to absorb the EM wave more than 20dB over the frequency band.
The ferrite tile in a single layer type has been used, the frequency band of which is about 30MHz ~ 400MHz, with more than 20dB of absorption capability. In the case of a grid type absorber developed by Y. Naito, the frequency range to satisfy the above absorption characteristics is approximately from 30MHz ~ 870MHz. Thus it was not sufficient to satisfy the above condition.
Accordingly, in this dissertation, in order to satisfy the above demand, the electromagnetic wave absorbers with wide band characteristics was proposed by controlling shape and dimension. The proposed electromagnetic wave absorber in cutting cone-shaped one is of less than 5cm in thickness. The bandwidth of the proposed absorber is from 30MHz to 6GHz, which was designed by the EMCM and confirmed by simulation and experiments.
As a measuring method of the absorption characteristics of the ferrite electromagnetic wave absorber, tapered rectangular coaxial line, was fabricated and used, which has 50Ω adapter with l3/8 in diameter.
In addition, the characteristics of the anechoic chamber by the proposed cross-shaped absorber were evaluated be the image method. They were compared with those of the OATS.